HR: 0800h
AN: A21B-0843    [Abstracts]
TI: The Effect of Fire and Drainage on CO₂ Fluxes in Black Spruce Stands of Interior Alaska
AU: * ODonnell, J A
EM: ftjao1@uaf.edu
AF: Institute of Arctic Biology University of Alaska Fairbanks, 311 Irving I University of Alaska Fairbanks, Fairbanks, AK 99775 United States
AU: Harden, J W
EM: jharden@usgs.gov
AF: United States Geological Survey, 345 Middlefield Rd ms 962, Menlo Park, CA 94025 United States
AU: Pruett, L E
EM: lpruett@usgs.gov
AF: United States Geological Survey, 345 Middlefield Rd ms 962, Menlo Park, CA 94025 United States
AU: Manies, K L
EM: kmanies@usgs.gov
AF: United States Geological Survey, 345 Middlefield Rd ms 962, Menlo Park, CA 94025 United States
AB: Soil thermal and moisture conditions function as important controls on the flux of carbon dioxide (CO2) at the soil-atmosphere interface. In the boreal forest, the interaction between fire and permafrost plays an important role in regulating soil thermal properties and drainage. Fire typically warms soil temperature by reducing summer albedo and temporarily removing shading. The presence of permafrost restricts infiltration of soil water to deeper mineral horizons. Seasonal thawing of soil in the active layer allows for increased drainage of surface soils. We used a full factorial design to examine the effect of fire (burned and unburned) and drainage (upland and lowland) on CO₂ fluxes. This study was conducted following a wildfire in July 2003 in four black spruce stands near Ericson Creek, a small drainage approximately 150 km north of Fairbanks, Alaska. We measured rates of net ecosystem exchange (NEE) and ecosystem respiration (ER) in conjunction with soil thermal and moisture properties. Fire significantly lowered net ecosystem carbon uptake (NEE) rates in the lowland stands, with burned stands emitting 0.71 gC m^-2 d^-1 and unburned stands taking up 0.62 gC m^-2 d^-1 and over the summer. However, fire did not significantly alter rates of NEE in the upland sites. Drainage conditions significantly altered rates of ER, averaging 0.94 gC m^-2 d^-1 in the two upland sites, nearly half the observed rates in the two lowland sites. Thaw depth increased seasonally in all four sites, with the greatest change occurring in the upland burn site. In the lowlands, thaw depth was shallower in the burned site than the unburned site, whereas in uplands, thaw depth was deeper in unburned sites. It appears that reduction in organic layers reduces winter insulation more effectively than summer insulation in the wet lowlands (i.e. thaw is shallower in burned site), whereas the reverse is true for the drier uplands (i.e. thaw is deeper in burned sites). These landscape controls over thermal processes (drainage, fire) appear to regulate the response of carbon dioxide fluxes in this system.
DE: 0428 Carbon cycling (4806)
DE: 0475 Permafrost, cryosphere, and high-latitude processes (0702, 0716)
DE: 0702 Permafrost (0475)
DE: 1631 Land/atmosphere interactions (1218, 1843, 3322)
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005